The present invention relates to a display driver, an electro-optical device, and an electronic instrument.
As a liquid crystal display (LCD) panel (display panel in a broad sense; electro-optical device in a broader sense) used for an electronic instrument such as a portable telephone, a simple matrix type LCD panel and an active matrix type LCD panel using a switch element such as a thin film transistor (hereinafter abbreviated as “TFT”) are known.
The power consumption of the simple matrix type LCD panel can be easily reduced in comparison with the active matrix type LCD panel. However, it is difficult to increase the number of colors and display a video image using the simple matrix type LCD panel. The active matrix type LCD panel is suitable for increasing the number of colors and displaying a video image. However, it is difficult to reduce the power consumption of the active matrix type LCD panel.
The simple matrix type LCD panel and the active matrix type LCD panel are driven so that the polarity of the voltage applied to a liquid crystal (electro-optical material in a broad sense) forming a pixel is alternately changed. As such an alternating driving method, a line inversion driving method and a field inversion drive (frame inversion driving) method are known. In the line inversion driving method, the polarity of the voltage applied to the liquid crystal is reversed in units of one or more scan lines. In the field inversion driving method, the polarity of the voltage applied to the liquid crystal is reversed in field (frame) units.
In this case, a method of changing a common electrode voltage (common voltage) supplied to a common electrode opposite to a pixel electrode forming a pixel at the inversion drive timing can reduce the voltage level applied to the pixel electrode.
When using the above alternating driving method, power consumption is increased accompanying charging and discharging the liquid crystal. In order to solve this problem, JP-A-2002-244622 discloses technology of reducing power consumption by initializing charges stored in the liquid crystal to zero by short-circuiting two electrodes provided on either side of the liquid crystal during inversion drive, thereby causing the voltage to transition to the intermediate point of the voltage before short-circuiting the electrodes, for example. JP-A-2004-354758 discloses technology of reducing power consumption by reducing a change in potential of a source line when changing a common electrode voltage by applying a precharge potential to the source line in a first precharge period before a pixel electrode write period and a second precharge period before changing the common electrode voltage.
However, the technologies disclosed in JP-A-2002-244622 and JP-A-2004-354758 have a problem in which the effect of reducing power consumption varies depending on the voltage applied to the source line. Therefore, the effect of reducing the amount of charges by charging and discharging the common electrode of which the polarity of the voltage is reversed may be insufficient. According to the technology disclosed in JP-A-2002-244622, the amount of charging and discharging may be increased by short-circuiting the electrodes provided on either side of the liquid crystal depending on the relationship between the voltage applied to the source line and the polarity of the common electrode voltage, whereby the effect of reducing power consumption may be impaired.
Therefore, when recycling supplied charges, it is desirable that the source line and the common electrode be driven while reliably reducing power consumption using a simple configuration.
On the other hand, priority may be given to a reduction in chip size and mounting area of a display driver and the like at the expense of the effect of reducing power consumption to some extent depending on the application field of the display driver. This applies to the case of applying a display driver and the like to a product for which the customer (manufacturer of electronic instrument) desires to reduce the cost of a display driver or an LCD panel including the display driver, for example.
Therefore, it is desirable that a display driver and the like be provided which make it possible to give priority to a reduction in power consumption or a reduction in cost corresponding to the customer's demand. Specifically, it is desirable that power consumption be minimized at the expense of a cost reduction effect to some extent (priority is given to reduction in power consumption) or cost be minimized at the expense of a power consumption reduction effect to some extent (priority is given to reduction in cost) using a simple configuration. It becomes possible to satisfy various users' demands using one type of display driver by providing such a display driver and the like, whereby the manufacturing cost can be further reduced.